DIN switches between German Umlauts and international characters like the square brackets and signals the keyboard's state with an LED. If you try to use Umlauts in international mode or vice versa, you get buzzed. Acoustically.

The keyboard is set for a serial connection at 9600 baud ... this can be changed with the DIP switches visible in the photos. The "Kontron 80 Bedienungsanleitung" also covers the PSI98's keyboard.

I can't test the keyboard until next week, but I'll check if the other documents give more hints.

I've fixed some more issues and added proper DMA support, CP/M can now successfully load the SETCRT program:

The driver was also committed to the repository.

rfka01: There are checksums printed on the ROMs, however except for the keyboard ROM they don't match the files. If it's not too much trouble, maybe you can try a redump and see if you get another result? Or maybe the labels are just wrong, since I don't see any obvious errors.

Duke, the dumps of the three mainboard ROMs turn out exactly like the first try when I run them through my second eprom programmer, so it would appear that my dumps are correct, maybe they updated the ROMs later but didn't bother do correct the labels - or the ROMs have become corrupt.

There's one thing I noticed, though:

Using the HxD hex editor, I generated different types of checksums for the ROMs ... at least the keyboard ROM (mcg_2.1_1035_06f0.bin) has a valid Checksum-16 (not CRC-16) of 06f0.